Hydrocarbonaceous compositions, such as petroleum (crude oil) and fuels, almost always contain moisture. Additional water can accumulate in tanks as atmospheric moisture condenses. Moisture accumulates in diesel tanks, for example, as condensate droplets on exposed tank surfaces, as dissolved water in the fuel and as water bottoms beneath the fuel. Similarly for petroleum, water can condense and accumulate in pipelines. Alcohol/fuel mixtures, such as “gasohol,” tend to absorb and retain higher concentrations of water than does alcohol-free petroleum-based fuel. In addition, more recently, water has begun to be deliberately incorporated into fuel for environmental benefits. It has been found that internal combustion engines, especially diesel engines, that employ water-fuel emulsions can produce lower nitrogen oxides, hydrocarbons and particulate emissions. Reducing emissions from vehicles has been driven by governmental and environmental concerns and so it is expected that the use of aqueous hydrocarbon fuel emulsions will increase.
The presence of water in hydrocarbonaceous compositions, either through deliberate introduction (e.g. emulsified fuel), or through condensation (e.g. in storage or transportation vessels), can, however, lead to problems. Because microbes depend on water for survival, water in the hydrocarbonaceous compositions can cause microbial contamination. Microbes depend on the organic molecules in these compositions for nutrition and growth. Consequently, some species attack the compositions directly, growing at the expense of hydrocarbon and non-hydrocarbon components.
The biodegradation of fuel, in support of microbial growth, is a direct cause of fuel contamination. Color, heat of combustion, pour point, cloud point, thermal stability, detergent and anti-corrosive properties adversely change as microbes selectively attack fuel components. In addition to loss of additive and fuel performance, as bacteria and fungi reproduce, they form biomass, which accumulates at the fuel:water interface, on tank surfaces and on filters. In the case of crude oil, microbiologically influenced corrosion can occur in pipelines as a result of the activity and growth of sulfate reducing bacteria (SRB).
Corrosion issues can also be influenced by the presence of water and acids in hydrocarbonaceous compositions. Biodiesel fuel, in particular, contains free fatty acids and petroleum-derived fuels typically contain residual naphthenic acids and sulfur which can react with water vapor during combustion to form sulfuric acid. While removal of sulfur and acids from fuel is possible, this introduces additional process costs for the fuel manufacturer. In addition, lubricants that are based on phosphoric and carboxylic acids are deliberately added to some fuels (e.g. fuel emulsions) to improve performance. In crude oil, in addition to microbiologically influenced corrosion, the presence of dissolved carbon dioxide (carbonic acid) and/or hydrogen sulfide can also lead to corrosion issues.
In view of the foregoing, a need exists in the art for additives that assist in limiting corrosion and/or microbial growth in hydrocarbonaceous compositions.